1. Field of the Invention
This invention relates to guard plates which fit over a door in the area where the lock is mounted in order to increase the horizontal impact resistance of the door.
2. Description of the Prior Art
It is known in the art to provide a U-shaped plate which surrounds the edge of a door and which has openings through which the inside and outside doorknobs and/or a deadbolt unit extend. These U-shaped plates may be provided for either decorative or security purposes. Plates of this type are disclosed in U.S. Pat. Nos. 950,926 to Keil, 3,666,309 Zarzycki, 3,673,605 to Allenbaugh, 4,139,999 to Allenbaugh and 4,141,234 to Hoos.
By utilizing guard plates of the above described type, doors which normally have relatively low security with respect to retaining a lock within the door, such as hollow pine doors, can in effect be strengthened so that the lock mounted in such doors can withstand relatively high horizontal impact forces. These U-shaped guard plates are thus useful both in reducing the cost of doors which must meet particular strength standards and also for increasing the horizontal impact resistance (e.g., resistance to kicking or shoulder impact) of existing doors in the area of the lockset.
One problem with the use of the above described U-shaped guard plates with existing doors (i.e., as an aftermarket device) is the possibility that their installation will cause misalignment between the lock bolt of the door and the striker plate located on the door frame and through which the lock bolt extends. In many instances, the initial installation of a door is such that when it is closed, it will rest against a door stop, as shown in FIG. 1 of the drawings. The installation of a U-shaped guard plate causes the closed position of the door to move slightly away from the doorstop, which may in turn prevent the lock bolt from properly fitting into the opening in the strike plate carried in the door frame. This situation is illustrated in drawing FIG. 2. Therefore, the use of a U-shaped guard plate is not always possible unless the strike plate and the opening beneath it are repositioned.
The primary object of the present invention is to provide a guard plate which strengthens a door in the area of the lock assembly and does not present any problems with respect to misalignment of the lock bolt caused by installation of the guard plate.
Another object of the present invention is to provide a guard plate which enables softwood doors to meet strength standards which normally can be met with only metal or hardwood.
A further object of the invention is to provide a guard plate which is configured to resist forced rotation of a deadbolt lock to thereby improve the security of such a lock.